Research On Real-time Rendering Technology Of Large Scale Terrain Based On LOD And Motion Prediction

Along with the development of computer technology, graphics and image technology, Visualization of large-scale terrain plays an important role in geography information system(GIS), simulation system, visual reality and 3D games, etc. It is a core part of an outdoor scenes rendering engine and also is one of the hot topics in Computer Graphics research field. When we want to generate a scene with quite a lot of reality, the requirement of real-time response in interactive operations is not be satisfied because of the complexity of the scene. At the same time, the scheduling between the inner and outer stored of massive terrain data is a new challenge for real-time rendering. In order to improve the speed and make sure the performance of real-time, the algorithm of LOD and efficient scheduling is used in the terrain reading to simplify the terrain models and reduce the the difference of speed between the inner and outer stored.Level of Detail(LOD) is a technology that accords with people’s sense of vision characteristic to gradually simplify the scenery’s surface details, which can reduce the scene’s geometry complexity and improve the rendering speed. In interactive time of real time, according to the location and line of sight got along by current moment of the eyes, we adopt the high-accuracy model in close area and low-accuracy in far area, so that we can rightly deal the contradiction between the sense of reality and rendering speed, and improve the rendring speed of the large-scale terrain at prior condition that does not affect the visual effect of the scene. The technology can effectively solve the contradiction between the visual picture effect and the speed of the large-scale terrain rendering.In this dissertation, the algorithm of LOD and scheduling are studied systematically, and the LOD generation algorithm based on the error screen combined with data structure and terrain block and hierarchy are proposed. At the same time, the pre-scheduling strategy is adopted to deal the difference of speed between the inner and outer stored, which can improve the terrain can be rendered efficiently. And the main contents are listed as follows:1. Key technologies in LOD Large-scale terrain real-time rendering are researched. At the same time, Relative technologies are presented such as: LOD of the terrain, visibility culling, LOD error, technologies of texture, disk scheduling etc.2. By researching the existing LOD algorithm based on Quad tree, this paper proposes a LOD algorithm based on Enclosing Ball Screen Error of Quad-tree. In this algorithm, the terrain is divided into preprocessing stage and real-time rendering stage. In the preprocessing phases, the algorithm builds the enclosing ball for every terrain block to reduce the data storage and computation. In real-time rendering stage, it establishes LOD model based on enclosing ball and implements the real-time rendering for large-scale terrain, according to the viewing frustum culling based on projection and bounding sphere to loading terrain blocks, combined with the data structure of quad-tree to build bounding spheres. Experiments results show that the method can improve the frame rate to ensure smooth large-scale terrain rendering and the performance of real-time.3. The method of viewpoint prediction based on Hermite is proposed, based on the new LOD algorithm. Hermite interpolation algorithm is used to predict viewpoint movement, so that the frame rate is improved effectively and the rendering is steady. Compared with other algorithms, this method is more stable, and calculation is smaller. The Runge phenomenon is avoided when an appropriate step size is chosen. The experiments show that the variation of frame rates is small when the large-scale terrain is being rendered; the terrain rendering speed is increased, and avoid the visual sense of the jumping.